It looks like you have applied for the wrong duration of the visa, and in cases like this the result is usually that they approve the application for the correct duration but keep the application fee.
The guidance (pdf) says
Periods of grant
Partners: We will grant leave in line with the expiry date of the Main Applicant’s leave, except where the Main Applicant has been granted indefinite leave to remain. In these cases, we will grant you a period of three years leave. An application for further leave may then be made if required to take you up to the applicable qualifying period for indefinite leave to remain.
Children: We will grant leave in line with:
(i) a period which expires on the same day as the leave granted to the parent whose
leave expires first, or
(ii) Where both parents have, or are at the same time being granted, indefinite leave to
remain, or have since become British citizens, leave to remain will be granted to the
applicant for a period of 3 years.
If the online application portal did not allow you to make an application for a three year visa then you can submit a complaint to UKVI, but I suppose it's unlikely that they will refund the money; they will more likely argue that you should have made the complaint before paying the fee.
Following UK immigration news in the media, I see that some people have had some luck by involving their MP. If I were you, and the response to the complaint proves unsatisfactory, I would try that.